Field of the Invention
The present invention relates to a drawing method and a servo press system, and more particularly, to a technique for deep drawing a material by use of a servo press which transmits a drive force to a slide from a servo motor via a link mechanism.
Description of the Related Art
There has been conventionally proposed an automatic slide position control apparatus for a servo press which enables a servo press with relatively small forming energy to perform forming that requires large energy (Japanese Patent Application Laid-Open No. 11-254197).
The automatic slide position control apparatus for a servo press lowers a slide at a set load, returns (raises) the slide by a given dimension when the slide stops with the forming changed from a dynamic friction to a static friction, and thereafter re-pressurizes the slide to advance the forming with a dynamic friction. By repeating the up-and-down operation of lowering and raising the slide (the lowered amount>the raised amount) as described above until a forming amount reaches a target forming amount, the required forming amount can be ensured even when a servo motor has small output energy.
There has been also proposed a press forming method for a metal plate in which an operation of separating a blank holding plate from a metal plate when a press load reaches a predetermined value or more, and thereafter sandwiching the metal plate between the blank holding plate and a die again by use of a punch and the die to effect forming is performed at least one time in the course of a stroke for performing drawing (Japanese Patent Application Laid-Open No. 2008-23535).
In accordance with the press forming method for a metal plate, a lubricant restores its film thickness by separating the blank holding plate from the metal plate, and slidability is restored when the operation of forming the metal plate by use of the same punch, die and blank holding plate is started again. Therefore, the occurrence of a crack in the metal plate and the occurrence of galling can be suppressed.
Moreover, there has been proposed a vibration forming method for a direct-acting press which performs forming while subjecting a slide to repetitive motion of lowering and raising the slide, in which in a raising step in the repetitive motion, a slide load is returned to a smaller value than that in a lowering step, and held for a predetermined time with a top die in abutment against a material to be processed (Japanese Patent No. 3685615).
In accordance with the vibration forming method for a direct-acting press, marking is performed without separating the top die and the material to be processed during vibration forming, so that displacement between the top die and the material to be processed is not generated between a start time and an end time of the vibration forming. The top die and the material to be processed are not repeatedly contacted and separated, so that noise generated when the top die touches the material to be processed is eliminated, thereby improving a working environment, and suppressing a decrease in the operating life of the die.